A simple assembly code for the 8086 microprocessor to display a digital clock in real time.

clock.asm

.model small
.stack 1024
.data
.code
start:
  mov ax,@data
	mov ds,ax
	extrn writesint:proc
	mov ah,2ch
	int 21h
	mov dl,ch
	add dl,48
	mov ah,2h
	int 21h
	mov ah,00h
	mov al,cl
	mov bl,cl
	call writesint
	mov dl,dh
	mov al,dh
	call writesint
	add bl,10
	looper:
		mov ah,2ch
		int 21h
		mov ah,00h
		mov al,ch
		call writesint
		mov ah,00h
		mov al,cl
		call writesint
		mov dl,dh
		mov al,dh
		call writesint
		mov cx,01
		mov dx,00
		mov ah,86h
		int 15h
		mov ax,00h
		int 10h
		cmp cl,bl
		jnz looper
	mov ah,4ch
	int 21h
	end start
end

ioasm.asm

.MODEL SMALL
.DATA
TempStr  db   1,2           ; temporary storage for STDIN input
t2       db   80 dup (0)     
t3       db   13,10,'$'      
Letters  db   '0123456789'  ; possible characters
CrLf     db   13,10,'$'     ; carriage return and linefeed
.CODE
PUBLIC readsint,writesint
readsint PROC           ; reads an integer into the AX register
   push bx              ; save all registers used
   push cx
   push dx
   push si
   mov  TempStr,80      ; read in string using buffered STDIN function
   mov  ah,0Ah
   lea  dx,TempStr
   int  21h
   mov  cl,TempStr+1    ; get length of string
   xor  ch,ch
   mov  bx,0            ; initialize digit index 
   mov  ax,0            ; initialize running total
   mov  si,10           ; radix = decimal = 10
startmul:
   mul  si              ; move total one place to the left
   xor  dh,dh
   mov  dl,[bx+t2]      ; get next digit
   sub  dl,48           ; ascii --> integer value
   add  ax,dx           ; add digit to total
   inc  bx              ; increment digit index
   loop startmul
   push ax
   mov  ah,09h          ; output carriage return/linefeed
   lea  dx,CrLf
   int  21h
   pop  ax
   pop  si              ; restore registers
   pop  dx
   pop  cx
   pop  bx
   ret                  ; return to point of call
readsint ENDP
writesint PROC       ; outputs the integer in the AX register
   push ax              ; save all registers used
   push bx
   push cx
   push dx
   push si
   mov  bx,10           ; radix = decimal = 10
   xor  si,si           ; initialize digit counter 
startdiv:
   xor  dx,dx
   div  bx              ; divide no by 10
   push dx              ; save remainder
   inc  si              ; increment digit counter
   cmp  ax,0            ; check for end of divisions
   jne  startdiv
   mov  cx,si           ; set digit counter
   mov  bx,0            ; initialize position counter
makeletters:
   pop  ax              ; get digit
   add  al,48           ; make integer --> ascii value
   mov  [t2+bx],al      ; insert digit into string
   inc  bx              ; increment position counter
   loop makeletters
   mov  [t2+bx],'$'     ; put end-of-string marker
   mov  ah,09h          ; output integer as string
   lea  dx,t2
   int  21h
   mov  ah,09h          ; output carriage return/linefeed
   lea  dx,CrLf
   int  21h
   pop  si              ; restore registers
   pop  dx
   pop  cx
   pop  bx
   pop  ax
   ret                  ; return to point of call
writesint ENDP
END

extrn writesint:proc
emu8086 tell me that erorr

for hassanfattah ...... remove the two dots (:) and call extrn ... because the proc name is extrn not writesint or write as ( extrn far proc )

can uh explain how the programme can run?

Circuit diagram please